In the gasification of solid carbonaceous source material such as coal, char, and coke, a metal oxide particularly such as zinc oxide, is employed to provide the necessary oxygen. Such techniques are disclosed in U.S. Pat. Nos. 2,592,377 and 2,602,809.
In these processes, a finely divided solid particle-form carbonaceous material is admixed with zinc oxide as the oxygen carrier or oxygen donor in a reaction which can be illustrated by: EQU C+ZnO.fwdarw.Zn.uparw.+CO.uparw..
The reactants to the left are solid materials. The products to the right are gaseous materials. Zn vapor forms in the gasification of the carbonaceous material. Heretofore, it has been necessary to cool the gaseous reaction products, subsequent to the gasification step, to separate the Zn as a molten metal, from the gaseous CO carbon monoxide, which is the desired product.
Heretofore, the condensed molten Zn has been reoxidized in an oxidation step, which converts the molten zinc back to gaseous zinc, and then reacts the gaseous zinc with air as the oxygen source to reform the zinc oxide to recycle to the gasification step for further contact with char.
As can be realized, the cooling requirements for condensation of the gaseous zinc to molten zinc for separation of the carbon monoxide product, and the heating requirements for revaporization of the molten zinc in order to reoxidize it, have been energy intensive steps and pose literal economic barriers to the development of the zinc oxide processes. Furthermore, during cooling of the zinc/carbon monoxide gas to obtain molten zinc metal, some formation of zinc oxide has been a slight but obstinate result. Apparently, some reversion to the oxide zinc occurs with consequent loss of a portion of the desired carbon monoxide, forming what sometimes has been termed a "blue powder" in zinc collection chambers, leading to line plugging and other difficulties.
Needed has been a straight-forward method of reoxidation of the zinc to zinc oxide, with minimization of energy requirements.